Question

A student runs two experiments with a constant-volume "bomb" calorimeter containing 1200. g of water (see sketch at right). thermometer stirrer water First, a 8.000 g tablet of benzoic acid (C H CO,H is put into the "bomb" and burned completely in an excess of oxygen. (Benzoic acid is known to have a heat of combustion of 26.454 kJ/g.) The temperature of the water is observed to rise from 12.00 °C to 48.74 °C over a time of 11.3 minutes. insulation Next, 5.930 g of ethylene (C,H,) are put into the "bomb" and similarly completely burned in an excess of oxygen. This time the temperature of the water rises from 12.00 °C to 63.95 °C. chemical reaction "bomb Use this information, and any other information you need from the ALEKS Data resource, to answer the questions below about this reaction: A "bomb" calorimeter. C2H2(g) + 3O2(g) → 2 CO2(g) + 2H2O(g) Be sure any of your answers that are calculated from measured data are rounded to the correct number of significant digits. Note for advanced students: it's possible the student did not do these experiments sufficiently carefully, and the values you calculate may not exactly match published values for this reaction. exothermic Is this reaction exothermic, endothermic, or neither? endothermic x 6 ? neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in the second experiment. [kJ Calculate the reaction enthalpy AH Ex per mole of C2H4 mol

Answer 1

The reaction is exothermic

The heat evolved in the combustion reaction of ethylene is 622 kJ

Reaction enthalpy

$\Delta$Hrxn = $\Delta$ Hproducts - $\Delta$ Hreactants

           = {[(2mole)(393.5) + 2 (285.8)] - [(52.47) + (0)]}

        = 787 + 571.6 -52.47

          = 1306.13 kJ/mol